1. Field of the Invention
The present invention relates generally to an electrochemical sensor used for the quantification of a specific component or analyte in a liquid sample. Particularly, the present invention relates to an electrochemical sensor for the detection of analytes present in biological fluids. More particularly, the present invention relates to a disposable electrochemical sensor for the in vitro detection of oxygen concentration.
2. Description of the Prior Art
Oxygen is an essential factor to aquatic life and human beings. The quantification of the content of oxygen in the blood is extremely important in clinical chemistry and other fields. Various optical methods have been investigated for the detection of dissolved oxygen concentration based on the dynamic quenching of fluorescent or phosphorescent materials. Electrochemical methods, however, are more attractive due to their high sensitivity, simplicity and inexpensive detection equipment. Thus, much attention and effort has been expended to developing electrochemical devices.
Biosensor history generally began in the early 1960s and the progenitor of the biosensor was an American scientist named L. C. Clark. Clark had studied the electrochemistry of oxygen reduction at platinum metal electrodes, pioneering the use of a platinum metal electrode as an oxygen sensor. In fact, platinum electrodes used to detect oxygen electrochemically are often referred to generically as “Clark electrodes.”
U.S. Pat. No. 4,311,151 (1982, Hagihara) is one example of a well-known electrochemical oxygen sensor similar to the conventional Clark electrode. Hagihara discloses an oxygen measuring electrode assembly for transcutaneous measurement of the partial pressure of oxygen in arterial blood. The assembly includes an anode, a cathode that has a thin ring surface or circularly-bounded field of dot-shaped surfaces and an insulating electrode holder, a disposable tubular member holder fixedly holding the periphery of an oxygen permeable hydrophobic electrode membrane, and a skin-heating part including a heat-conducting block that is thermally connected to a heater and a temperature detector. Oxygen permeates through a gas permeable hydrophobic membrane from the blood sample into an internal electrolyte solution where it is reduced at the cathode. The oxygen reduction current, measured amperometrically, is proportional to the dissolved oxygen concentration.
Further development work of the “Clark” type electrode by J. W. Severinghaus et al. led to the development of a practical electrochemical oxygen sensor for clinical use.
Recently, P. D'Orazio et al. (Clinical Chemistry 43, 1804-1805, 1997) reported a planar amperometric oxygen sensor. A polymeric perfluorinated ionomer available from Sigma-Aldrich under the trademark Nafion® can be used as an internal electrolyte and is spin-coated along with a custom-made, patented polymer.
Potentiometric oxygen gas sensors have also been devised. U.S. Pat. No. 6,663,756 (2003, Lee et al.) discloses a microchip-based oxygen gas sensor based on differential potentiometry. The working electrode is a cobalt-plated electrode, a buffered hydrogel, and an ion selective gas-permeable membrane. The reference electrode is a silver chloride electrode with the same ion selective gas-permeable membrane. By taking advantage of the corrosion potential, the microchip-based oxygen gas sensor measures the content of dissolved oxygen in a sample solution.
Chemical sensors for clinical blood analysis have been widely studied. The theory and practice as well as history of electrochemical sensors for clinical measurement of blood gases were well reviewed by C. E. W. Hahn (Analyst, 123, 57R-86R, 1998). Previously reported oxygen sensors, however, require a relatively large volume of blood.
To be usable as a clinical sensor, the sensors should give an easy, accurate analysis of a sample and be economical. Point-of-care and high sensitivity are also required for allowing health care personnel to perform analysis with a small volume of blood, which is especially important for infant patients.
Therefore, what is needed is an oxygen sensor that can be used to measure dissolved oxygen accurately and precisely with a minimum quantity of sample volume. What is also needed is an oxygen sensor that is disposable.